1. Field of the Invention
The present invention relates to a wall-mounted microwave oven and a method for controlling a hood motor, and more particularly, to a wall-mounted microwave oven and a method for controlling a hood motor to vary the speed of the hood motor.
2. Description of the Related Art
A wall-mounted microwave oven is installed on the upper wall over a gas range, and functions as a hood for inhaling vapor and fumes generated during cooking foods and discharging the inhaled vapor and fumes to the outside.
As shown in FIGS. 1 and 2, the wall-mounted microwave oven includes a main body 53 and a casing 56 enclosing the main body 53. Between the casing 56 and the main body 53 is formed a hood duct 65 as a path for discharging vapor and fumes. On the lower surface of the casing 56 is formed an inlet for inhaling vapor and fumes into the hood duct 65. On the upper surface of the casing 56 is formed an outlet 59 to which a discharging tube 61 is connected. The discharging tube 61 is connected to a discharging path 67 which penetrates through the wall and communicates with the outside. Also, on the upper portion of the main body 53 adjacent to the outlet 59 is formed a hood fan 63 for discharging the vapor and fumes inhaled into the hood duct 65 via the inlet 58 to the outside via the outlet 59.
The hood fan 63 operates by a user's selection through a selection button provided in a control panel 35. As it being the case, a hood sensor 57 (FIG. 5) which turns on or off the hood fan 63 according to air temperature or smoke detection is provided to the inlet 58 of the hood duct 65 or the inside thereof, thereby controlling operation of the hood fan 63. Here, the hood sensor 57 is generally made of a bimetal.
FIG. 5 is a circuit diagram of a hood driver of a conventional wall-mounted microwave oven. The hood motor 95 is installed on an electric power line which connects first and second commercial alternating voltage (AC) electric power lines 51 and 52 in series which are extended from an external power source 55. On the electric power line where the hood motor 95 is installed, a hood fan switch 72 which turns on or off the hood motor 95 and a speed selection switch 73 for selecting a driving speed of the hood motor 95 at low or high speed are installed. Here, the speed selection switch 73 has a high speed contact 73a and a low speed contact 73b for turning on the hood motor 95, with a result that the hood motor 95 operates at high speed or at low speed. The speed selection switch 73 is normally connected to the low speed contact 73b.
Meanwhile, the hood sensor 57 is connected in parallel with the hood fan switch 72. As described above, the hood sensor 57 detects heat or gases transferred from a gas range 100 and is turned on when heat or gases are detected.
By this configuration, a selection button for driving the hood fan can be selected to discharge heat and fumes emitted from foods during cooking. Here, if a user presses the selection button once, a microcomputer 60 turns on the hood fan switch 72, in which case the speed selection switch ordinarily in contact with the low speed contact 73b drives the hood motor 95 at low speed. If the selection button is pressed twice, the microcomputer 60 directs the speed selection switch 73 to contact the high speed contact 73a to drive the hood motor 95 at high speed. If the selection button is pressed once again, the microcomputer 60 turns off the hood fan switch 72 to stop the hood motor 95.
Although the user does not manipulate the selection button, the hood sensor 57 is turned on to drive the hood motor 95 at low speed If it detects heat or fumes during cooking.
However, the conventional hood motor 95 can be controlled only at two levels, that is, at low speed and at high speed. Thus, if a user wishes the hood motor 95 to be driven faster than at high speed, or wishes the hood motor 95 to be driven at intermediate speed, such user's needs cannot be met. That is, the driving speed of the hood motor 95 cannot be adaptively controlled according to the degree of heat or fumes emitted.
To solve these problems, the winding number of coils is increased to enlarge the capacity of the hood motor 95, thereby controlling the rotational speed of the hood motor 95 in multiple steps. In the case that the winding number of coils is increased, the volume of the hood motor 95 also increases. In addition, as the number of steps are increased, the number of contacts in the speed selection switch 73 should be increased. As a result, cost of production increases and an assembling work is complicated.